It depends on the person. Home Office statistics published today are expected to show a sharp rise in alcohol-related violent crime. Previous government figures show almost a quarter of assaults occurring in or near pubs and bars, and around half of violent crimes last year were thought to be committed while under the influence.

While most people aren't violent when drunk, says Klaus Miczek, professor of psychology at Tufts University, Massachusetts, a significant minority are.

Drunken violence is down to a range of neurological explanations, says Prof Miczek, and it's all down to the complex chemistry of the brain. Brain cells communicate with each other using electrical impulses, but these transmissions are regulated by a number of chemicals called neurotransmitters. Each of these binds to a specific receptor in the brain cell, and it is the behaviour of these receptors that, in some drinkers, is modified even by small amounts of alcohol. Scientists have not yet discovered which part of the receptor is linked with violence, says Prof Miczek.

Around one in five alcoholics are known as "type 2", says Miczek, and frequently prone to violent behaviour. The brains of type 2 alcoholics often have a different form of a key molecule, which stops the mood-regulating chemical serotonin, from being transported properly.

So why does alcohol have varying effects on different people's brains? Is it nature or nurture? "Genetics is too glib an answer," says Miczek. "Genes don't cause behaviour, they cause behaviour if they are triggered by a specific experience." Childhood experiences, for example, can have a huge effect in defining which genes actually manifest themselves later in life.

Robert Patton of the National Addiction Centre says it is not just perpetrators of violence who are affected by alcohol. The same mechanisms that make some people violent make other people take risks: it is not just the perpetrators that are drunk, but often the victims too.